This invention relates generally to systems for optically recording information signals on recording discs and, more particularly, to a system for recording information signals, such as video signals, by a laser beam which forms a plurality of pits on a recording disc.
In general, one known system for recording video signals on a recording disc, employs an optical recording system. The video signals are recorded by a laser beam which forms pits on the recording disc at pitch intervals which conform with the frequency of the signals.
In known optical recording systems of this character, the same light beam width is used in both the longitudinal and the transverse directions of the track. Each pit is the same, and the pitch intervals between the pits cannot be made very small since the circular laser beam spot is used. Consequently, higher frequency signals cannot be satisfactorily recorded.
Furthermore, the size of the spot on the recording disc which is exposed to the laser beam, in general, is greater than a specific value. Therefore, the recording depth of the pits becomes too deep, and the width of the pits correspondingly becomes too large. As a consequence, in these known systems, the exposure spot becomes larger, and the width of the pits in the longitudinal direction of the track becomes larger, in accordance with the frequency of the recording signal. If the size of the exposure spot becomes too large, the record surface around the peripheral edge parts of pits exceeds a specific value. Excavation of the peripheral edge takes place, and the pit width in the track transverse direction also becomes too large. For this reason, the pit width in the track transverse direction varies with the frequency of the recording signal, and the track pitch must be made too large. As a consequence, the rate of utilization of the recording surface of the recording disc has been poor. Moreover, a good reproduction of the recorded signal could not be achieved.